diff --git a/NEWS.md b/NEWS.md
index 03326003..76b5c232 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # bayesplot (development version)
 
+* Added dedicated unit tests for `param_range()`, `param_glue()`, and `tidyselect_parameters()` tidy parameter selection helpers.
 * Use `rlang::warn()` and `rlang::inform()` for selected PPC user messages instead of base `warning()` and `message()`.
 * Standardize input validation errors in `ppc_km_overlay()` and interpolation helpers to use `rlang::abort()` for consistent error handling.
 * Fix assignment-in-call bug in `mcmc_rank_ecdf()` (#).
diff --git a/tests/testthat/test-tidy-params.R b/tests/testthat/test-tidy-params.R
new file mode 100644
index 00000000..be2e73a0
--- /dev/null
+++ b/tests/testthat/test-tidy-params.R
@@ -0,0 +1,132 @@
+source(test_path("data-for-mcmc-tests.R"))
+
+# param_range --------------------------------------------------------------
+
+test_that("param_range selects correct parameters by index", {
+  all_pars <- c("alpha", "beta[1]", "beta[2]", "beta[3]", "sigma")
+  result <- param_range("beta", c(1, 3), vars = all_pars)
+  expect_equal(result, c(2L, 4L))
+})
+
+test_that("param_range returns empty integer when no matches", {
+  all_pars <- c("alpha", "gamma[1]", "gamma[2]")
+  result <- param_range("beta", 1:3, vars = all_pars)
+  expect_identical(result, integer(0))
+})
+
+test_that("param_range handles single index", {
+  all_pars <- c("alpha", "beta[1]", "beta[2]", "sigma")
+  result <- param_range("beta", 2, vars = all_pars)
+  expect_equal(result, 3L)
+})
+
+test_that("param_range drops non-matching indices silently", {
+  all_pars <- c("alpha", "beta[1]", "beta[3]")
+  # beta[2] does not exist, should be silently dropped
+  result <- param_range("beta", 1:3, vars = all_pars)
+  expect_equal(result, c(2L, 3L))
+})
+
+test_that("param_range errors when vars is not NULL or character", {
+  expect_error(
+    param_range("beta", 1:3, vars = list("a", "b")),
+    "'vars' must be NULL or a character vector."
+  )
+  expect_error(
+    param_range("beta", 1:3, vars = 1:5),
+    "'vars' must be NULL or a character vector."
+  )
+})
+
+# param_glue ---------------------------------------------------------------
+
+test_that("param_glue selects correct parameters with one expression", {
+  all_pars <- c("alpha[1]", "alpha[2]", "alpha[3]", "sigma")
+  result <- param_glue("alpha[{i}]", i = c(1, 3), vars = all_pars)
+  expect_equal(result, c(1L, 3L))
+})
+
+test_that("param_glue selects correct parameters with multiple expressions", {
+  all_pars <- c(
+    "b[X:1]", "b[X:2]", "b[Y:1]", "b[Y:2]", "sigma"
+  )
+  result <- param_glue("b[{var}:{lev}]", var = c("X", "Y"), lev = c(1, 2),
+                       vars = all_pars)
+  expect_equal(result, c(1L, 3L, 2L, 4L))
+})
+
+test_that("param_glue returns empty integer when no matches", {
+  all_pars <- c("alpha", "sigma")
+  result <- param_glue("beta[{i}]", i = 1:3, vars = all_pars)
+  expect_identical(result, integer(0))
+})
+
+test_that("param_glue drops non-matching names silently", {
+  all_pars <- c("b[X:1]", "b[Y:2]", "sigma")
+  # b[X:2] and b[Y:1] don't exist
+  result <- param_glue("b[{var}:{lev}]", var = c("X", "Y"), lev = c(1, 2),
+                       vars = all_pars)
+  expect_equal(result, c(1L, 2L))
+})
+
+test_that("param_glue errors when vars is not NULL or character", {
+  expect_error(
+    param_glue("alpha[{i}]", i = 1:3, vars = list("a")),
+    "'vars' must be NULL or a character vector."
+  )
+  expect_error(
+    param_glue("alpha[{i}]", i = 1:3, vars = 42),
+    "'vars' must be NULL or a character vector."
+  )
+})
+
+# tidyselect_parameters ----------------------------------------------------
+
+test_that("tidyselect_parameters selects by name", {
+  all_pars <- c("alpha", "beta[1]", "beta[2]", "sigma")
+  selected <- tidyselect_parameters(all_pars, vars(alpha, sigma))
+  expect_equal(selected, c("alpha", "sigma"))
+})
+
+test_that("tidyselect_parameters works with tidyselect helpers", {
+  all_pars <- c("alpha", "beta[1]", "beta[2]", "sigma")
+  selected <- tidyselect_parameters(all_pars, vars(starts_with("beta")))
+  expect_equal(selected, c("beta[1]", "beta[2]"))
+})
+
+test_that("tidyselect_parameters works with negation", {
+  all_pars <- c("alpha", "beta[1]", "beta[2]", "sigma")
+  selected <- tidyselect_parameters(all_pars, vars(-alpha))
+  expect_equal(selected, c("beta[1]", "beta[2]", "sigma"))
+})
+
+test_that("tidyselect_parameters errors when nothing matches", {
+  all_pars <- c("alpha", "beta[1]", "sigma")
+  expect_error(
+    tidyselect_parameters(all_pars, vars(starts_with("zzz"))),
+    "No parameters were found matching those names."
+  )
+})
+
+test_that("tidyselect_parameters works with contains()", {
+  all_pars <- c("b[(Intercept) X:1]", "b[(Intercept) X:2]", "sigma")
+  selected <- tidyselect_parameters(all_pars, vars(contains("Intercept")))
+  expect_equal(selected, c("b[(Intercept) X:1]", "b[(Intercept) X:2]"))
+})
+
+# Integration with vars() --------------------------------------------------
+
+test_that("param_range works inside vars() via prepare_mcmc_array", {
+  result <- prepare_mcmc_array(mat, pars = vars(param_range("beta", 1:2)))
+  pars <- dimnames(result)[[3]]
+  expect_equal(pars, c("beta[1]", "beta[2]"))
+})
+
+test_that("param_glue works inside vars() via prepare_mcmc_array", {
+  result <- prepare_mcmc_array(
+    mat,
+    pars = vars(param_glue("b[(Intercept) x:{i}]", i = c(1, 3)))
+  )
+  pars <- dimnames(result)[[3]]
+  expect_equal(pars, c("b[(Intercept) x:1]", "b[(Intercept) x:3]"))
+})